Cardiac stimulators typically include a pulse generator, limited power supply, electrical leads coupled thereto, and a controller. The controller typically includes a microprocessor having preprogrammed code, and may include ROM memory for storing programs to be executed by the controller and RAM memory for storing operands used in carrying out the computations by the controller. In order to maximize use of the limited power supply, it is desirable to set the pulse generator's stimulation output at the lowest output energy that reliably causes depolarization of the corresponding cardiac muscle.
To ensure the reliability of “capturing” a stimulation such as a pacing pulse, it is common practice to determine the minimum output energy that induces a cardiac depolarization (“the energy threshold”) manually during patient follow-ups, and then set the pacing pulse output at this minimum setting plus a wide error margin, oftentimes double or triple the minimum effective energy. This error margin is meant to account for the changes in energy requirements that may occur over time between patient follow-ups. Typically, when determining the energy threshold of the ventricles, both ventricles are simultaneously stimulated and if depolarization is detected, capture of both ventricles is assumed. It is expected to be far more efficient and/or economic for a pacemaker to determine a threshold for each chamber independently and adjust the output energy settings independently thereby incorporating a much smaller error margin.
For example, oftentimes a cardiac rhythm management device utilized for treating congestive heart failure delivers stimulation therapy to both sides of the heart for either atrial stimulation or ventricular stimulation. The sensing for depolarization signals from the corresponding chambers is non-discriminatory, such that if a depolarization signal is sensed, the device assumes capture in both chambers. The false assumption that the capture threshold is the same in both chambers may reduce the effectiveness of the stimulation therapy. Hence, there is a need for a device that verifies capture independently for stimulation pulses delivered to pre-determined chambers within an electrically continuous area of the patient's heart. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.